The present invention relates to centrifugal pumps and more particularly to a centrifugal pump with a variable capacity.
In order to form centrifugal pumps it is known to make use of combinations comprising a case having an axial inlet, a rotating impeller, extending from a rotatable shaft and journaled for rotation in case bearings, which includes a plurality of impeller vanes, and a radial output surrounding the tips of the impeller vanes and in fluid communication with a toroidal-shaped collecter which in turn outlets into a pump casing throat.
Variable capacity centrifugal pumps in various forms are already known and disclosed in U.S. Pat. Nos. to: Morris 4,417,849; Grennan 3,806,278; Grennan 3,918,831; Lynch 4,070,132; Bandukwala 4,378,194; Carlini 4,419,046; Morando 3,482,523; Rhoades 2,927,536; and French Patent No. 1,093,003.
A typical approach in providing a centrifugal pump with variable capacity involves varying the width of the impeller flow passages, impeller flow passages define the fluid passages between adjoining impeller vanes. This width adjustment of the impeller flow passage is initiated by measuring the existing back pressure in a casing throat and adjusting the impeller flow passage width, to either increase or decrease pump output to meet output demands, through an intermediate system. This intermediate system results in a less than ideal pump capacity adjustment in the responsive sense. Intermediate systems also add to the cost of the pump due to their complicated nature.
In Morando, a variable capacity centrifugal pump is shown wherein the variable capacity is controlled by attaching a movable shroud to a shaft which is concentric with the shaft which drives the impeller. The movable shroud is displaced by means of a piston attached to the shaft, the piston operative in a chamber substantially isolated from the rotating shroud. In Rhoades, a movable shroud also varies the capacity of the pump. As in Morando, the piston which causes translation of the shroud with respect to the impeller is operative in a chamber isolated from the functional area of the shroud, the movable shroud supported in rotation primarily by the casing and is engaged for rotation drive by the impeller. In French Patent No. 1,093,003, variable capacity is accomplished by mechanically displacing either the impeller or the movable shroud.